1. Field of the Invention
This invention relates, in general, to an apparatus and method for the silk-screen printing of each of the multiple curved surfaces of an article defined by multiple curved peripheral surfaces. In particular, the invention relates to apparatus and a method for the silk-screen printing of the peripheral, curved surfaces or panels on objects approximating triangular and rectangular cross-sections. More particularly, it relates to apparatus and a method for the silk-screen printing of the two sides of an article, e.g. a plastic bottle, having an oval-shaped cross-section, in a single pass.
2. Description of the Prior Art
The term "oval-shaped cross-section" as used herein is intended to cover articles, e.g., bottles, which have, in general, the cross-sectional shape of an oval. But, in a broader sense, the term "oval-shaped cross-section (oval-shaped)" is used to include all articles or objects having two opposed surfaces with a varying radius of curvature which is outwardly convex. The convex surface may be interrupted by flats or concave areas. Nevertheless, as will be appreciated hereinafter the invention is not limited to such oval-shaped articles; it includes articles having multiple curved surfaces defining its periphery, e.g., three, four, or even more curved surfaces of varying radius of curvature.
Cylindrical-shaped articles or objects, e.g. bottles, whether glass or plastic, having a circular or round cross-section can, in some cases, be silk-screen printed by merely rolling engagement of the bottle with the silk-screen surface. Thus, the frictional engagement of the article by the silk-screen is sufficient to cause rotation of the article in reasonably good registration with the screen, and without slippage. No positive registration means for rotationally driving the object to be printed in synchronism with the relative translatory movement of the silk-screen is required or provided in such cases. Nevertheless, in instances where close registration is required or where slippage between the bottle and screen might occur, a gear and rack, or simple round pully and cable, is conventionally used to provide the desired registration between the two.
In the silk-screen printing of the surface of an article having a varying radius of curvature such as a cylindrical-shaped bottle having an oval-shaped cross-section, this is not the case. The proper and positive registration between the surface of the article to be printed and the silk-screen is of critical concern, to prevent smudging of the printing ink on the surface being printed, i.e., the ink receiving surface. Thus, the curved surface of the bottle being printed must be maintained at a uniform linear velocity equal to the relative linear velocity of translation of the screen.
Any radius of curvature, as will be appreciated, defined by a relatively flattened bottle surface, e.g., that of an oval-shaped bottle compared to one having a circular-shaped cross-section, is much greater than a radius of rotation of the bottle about its own central axis. The curved surface of an oval-shaped bottle, moreover, only approximates that of a circle. Only a portion of any oval's curved surface is really the arc of a circle. Therefore, it is necessary to provide some positive drive means for moving the bottle's curved surface in synchronism with the linear translation of the screen, to prevent slippage with attendant blurring of the ink applied to the receiving surface.
Moreover, it is known to be absolutely necessary for satisfactory printing, i.e., sharp images, to provide that the squeegee or ink-knife in such a silk-screen printing process always be over the center of the circle circumscribed by the local radius of curvature of the ink receiving surface as the printing of the curved surface progresses. Thus, whether the squeegee is moved during the printing of the image or remains stationary while the silk-screen moves, or both the silk-screen and squeegee move, the squeegee must always be over the center of the circle circumscribed by the radius of curvature.
Thus, in the silk-screen printing of a bottle having an oval-shaped cross-section, to obtain a printed image that is relatively sharp, it is necessary to literally roll the surface to be printed over the working surface, i.e., the bottom surface, of the silk-screen. In other words, the local surface on the article being printed, i.e., that particular location on the surface receiving the printed image, must be rotated about its own center of curvature, at the same time that the bottle is being rotated about its longitudinal axis. As is well known, these centers are not concentric.
The printing of the curved or peripheral surfaces of an article having an oval-shaped cross-section has long been known. It is accomplished with the use or variation of one of three well known principles, e.g., (1) the screen moves horizontally, the squeegee being fixed and located above the center of the circle described by the oval section, i.e., ink receiving surface to be printed, the oval section being printed as it is rotated in synchronization with the screen translation, and in the same direction; (2) the screen is stationary, the squeegee being moved, the oval section being printed as it is rotated on the center of the circle described by the oval section, the squeegee and that center of curvature moving in the same direction; and (3) the oval-shaped article being printed, e.g., a plastic bottle, is rotated about its center on a vertically and horizontally oscillating fixture bar, the squeegee traveling in linear direction in synchronization with the center of the circle described by the oval section being printed, the screen being stationary. In a variation of the third method disclosed, the oval-shaped article is rotated about its center on a fixture bar that oscillates vertically as the squeegee travels in one direction in synchronization with the movement of the center of the circle described by the oval section being printed and in the same direction as the squeegee, the screen being moved in the opposite direction. Exemplary of prior art patents directed to the silk-screen printing of cylindrical-shaped articles having an oval-shaped cross-section are U.S. Pat. Nos. 3,109,365; 3,249,043; 3,260,194; 4,848,227; and French Patent Nos. 2,250,637; and 2,346,152.
U.S. Pat. No. 3,109,365 entitled "Stenciling Apparatus," which issued to William M. Karlyn on Nov. 5, 1963, and which was assigned to the Autoroll Machine Corporation, the assignee of the instant invention, discloses and claims a fixture bar which rotates the article to be printed, in approximate synchronism with the linear translation of the silk-screen. This is accomplished by means of a lost-motion connection between a crank arm affixed to the screen frame and a rod carrying the article. The variation in angular velocity of the article brought about by this device tends to offset the variation in the radius of curvature of the surface of the article being printed, at least to a limited extent, provided that the parts of the apparatus causing the lost-motion connection are properly proportioned. Nevertheless, such a silk-screen printing apparatus suffers from the fact that only a small variation in the radius of curvature of the surface to be printed is permissible. In practice, a silk-screen printing device of this construction can successfully label the portions of the oval which have a large and nearly uniform radius of curvature, but cannot pass the silk-screen around the more sharply curved parts. Although the apparatus of this patent is disclosed to be able to silk-screen print two successive articles upon each complete reciprocation of the silk-screen, the apparatus is, nevertheless, limited to the silk-screen printing of only one of the surfaces of each of the oval-shaped bottles, in one pass. In the event both surfaces are to be printed, the first is printed at one printing station, the ink dried, the bottle flipped over and then passed to a second printing station downstream for printing the other surface.
U.S. Pat. No. 3,249,043, entitled "Apparatus For Stenciling Oval Articles," and which issued to W. M. Karlyn et al, on May 3, 1966 is directed to apparatus which compensates for the variation in radius of curvature of an oval-shaped article. This is accomplished by maintaining an accurate inverse relationship of the angular velocity of the article being printed. Thus, an upwardly movable carrier, i.e. a fixture bar, is provided bearing a drive shaft, on which is mounted at one end a chuck for rotatably supporting the oval-shaped article to be printed and at the other end an oval-shaped gear for rotationally driving the article in synchronism with the linear velocity of a reciprocatory silk-screen. The oval-shaped gear has the same dimension and outline as that of the oval-shaped article to be printed. Thus, as the article is rotated in pressure engagement with the screen, the movable carrier which is pivoted at the end opposite from the drive shaft, accommodates a transverse movement of the chuck upwardly corresponding to the varying radius of the article, so as to keep its surface always in contact with the screen. Although the invention, as disclosed in this patent, is inoperable, it was later learned that one-sided printing of the oval-shaped object was possible. This is accomplished by keeping the single squeegee synchronized in a reciprocating relationship with the screen motion, using either well known mechanical or pneumatic means. Thus, following the principle well known to those in the silk-screen printing art, to keep the squeegee over the center of the circle described by the oval, this necessitated also moving the squeegee, and in a direction opposite to that of the screen. Nevertheless, it has not been found possible until now to print, in one pass, both sides of an oval-shaped object with the apparatus of that invention.
In U.S. Pat. No. 3,260,194 which issued to William M. Karlyn on Jul. 12, 1966, there is disclosed a registering drive mechanism which forms a positive driving connection between the screen frame and a bottle being printed. The mechanism includes in one case a clamp with adjustable jaws for gripping the base of the bottle being printed. In a modification of the mechanism for printing the surface of an oval-shaped bottle, the clamp includes a protrusion which is received in a mating recess in the base of the bottle. The bottle is supported in a cradle which is shaped to hold the bottle in registered relationship to the screen. The cradle is mounted on a rod, i.e. a spindle or drive shaft, disposed transversely to the direction of travel of the screen for oscillation about the rod axis as the screen passes over the bottle surface, the rod itself being rotatably mounted. For rotatably driving the clamp and bottle in synchronism with the silk-screen as the latter translates, a drive pinion is pinned to the spindle for the driving of the clamp, and meshed with a horizontally disposed rack. The rack forms one end of a four-bar parallelogram linkage including a pair of links and a drive bar. The drive bar of this parallelogram linkage is connected to a bar which is connected to the frame of the silk-screen. Thus, translation of the screen produces a corresponding translation of the rack and synchronized rotation of the pinion and bottle. This invention, although quite satisfactory for some purposes, is limited to the printing of only one curved surface of an oval-shaped bottle. Moreover, as is well known to those in the silk-screen printing art, in the printing of an oval-shaped surface, only that portion of the surface which describes a segment of a circle can be printed.
In French Patent No. 2,250,637 there is disclosed apparatus for the silk-screen printing of oval-shaped objects. The apparatus disclosed in this patent is believed to have a fixture bar that not only oscillates vertically but also horizontally. French Pat. No. 2,346,152 is believed to show an improved means over that disclosed in French Pat. No. 2,250,637, namely, a chain or cable and double grooved wheel, for causing rotation of the object on its center during the printing process.
It is known to provide a multiplicity of squeegees at one printing station. For example, in U.S. Pat. No. 3,251,298, there is disclosed the silk-screen printing of the body portion and neck portion of a cylindrical-shaped bottle, at one station. Thus, there are provided two squeegees and two screens in side-by-side relationship. Where two or more different imprints or colors are to be printed on the bottle, separate stations or locations are provided lengthwise of the silk-screen printing machine. As disclosed in U.S. Pat. No. 3,251,298, during printing, the two squeegees are moved in unison with the bottle being decorated, i.e. at the same constant linear velocity and in the same direction. The bottle is simultaneously rotated about its longitudinal axis in a direction opposite to its direction of travel. The body and neck screens are moved independently of one another, the body screen moving in the direction opposite to the direction of travel of the bottle during a printing operation, i.e., opposite to that of the squeegees.
Others patents of which I am aware, in addition to U.S. Pat. No. 3,251,298 have, heretofore, disclosed silk-screen printing apparatus wherein the silk-screen and squeegee or ink-knife are moved in opposite directions. Exemplary of such prior art are U.S. Pat. Nos. 4,005,649 and 4,245,554, in addition to the earlier disclosed U.S. Pat. No. 4,848,227.
U.S. Pat. No. 4,005,649 discloses a silk-screen printing machine wherein an object to be printed travels in a path, while being rotated about its axis, and which includes a movable printing screen and cooperating movable squeegee. The object to be printed, according to the patentee, will have only a single diameter, in general; however, objects wherein only a portion has a single diameter can also be printed. The bottle is caused to be rotated about its axis by a gear which is attached at the end of the shaft connected to the centering element of the bottle to be printed meshing with a horizontally disposed rack. According to the patentee, in the case where the object to be printed or the portion thereof to be printed has a diameter corresponding to double the diameter of the gear, the squeegee carriage and silk-screen carriages will be moved in opposite directions to one another.
U.S. Pat. No. 4,245,554 disclose a silk-screen printing machine wherein a web of material is printed with a succession of images. During the printing operation, the web is rolled against the silk-screen by a backing roller, which together with the ink-knife, i.e., squeegee, is moved in the opposite direction to the silk-screen.
In U.S. Pat. No. 4,848,227, which issued on Jul. 18, 1989, and entitled "DEVICE FOR THE SILK-SCREEN PRINTING OF CYLINDRICAL OBJECTS HAVING AN ELLIPTICAL CROSS-SECTION," there is disclosed a silk-screen printing apparatus wherein the silk-screen carriage and ink-knife or squeegee carriage both reciprocate back and forth in opposite directions. A horizontally disposed flat frame, like the fixture bar disclosed in the earlier above-mentioned U.S. Pat. No. 3,249,043, is mounted to pivot vertically upwardly at one end of the frame. At the other end is rotatably mounted, in transverse disposition, a spindle having at one end a chuck for holding the bottle to be printed. The other end of the spindle is fixedly connected to a toothed sector, which is mounted at its center to the bottom end of an elongated plate which extends vertically downwardly from the ink-knife carriage. The toothed sector which has a pitch circle diameter, according to the patentee, corresponding to the curvature of the cylindrical-shaped object to be printed, meshes with a horizontally disposed rack located on the bottom of the screen frame. The ink-knife carriage is connected to one end of a connecting rod, the other end of which is connected to a rocker arm which, in turn, is connected to the main drive. Thus, as the rocker arm rocks back and forth, the ink-knife carriage translates. This translatory motion causes the toothed sector to rotate back and forth which, in turn, causes the bottle to be printed to be rotated in likewise manner while at the same time being rotated on its own axis. As the toothed sector meshes with the rack provided on the silk-screen carriage, the silk-screen carriage is caused to move linearly back and forth in opposite direction to the translation of the ink-knife carriage. This opposite direction movement results from the fact that the spindle located on the flat frame is fixed horizontally, i.e., it cannot move in the horizontal direction of travel of the bottle being printed. The spindle can only move vertically upwardly and downwardly in an arcuate manner as the flat frame is pivoted vertically up and down.
Although the invention disclosed in U.S. Pat. No. 4,848,227 may be found quite satisfactory for certain silk-screen printing operations, its use is attendant with certain disadvantages. For example, the apparatus disclosed is not only limited to the silk-screen printing of only one surface of a bottle, it also is believed somewhat limited as to the curvature of the surface being printed, to obtain an image without some smudging. This is due to the fact that the toothed sector comprises a round cross-section while the bottle being printed is not of such a cross-section. Moreover, standard or available gears may not have the same radius as the segment of the circle described by the curved surface to be printed. As a result, those portions of the curved surface which vary from the radius of the standard or available gear are not printable. Further, only that portion or segment of the curved surface of an oval-shaped object that describes a circle can be printed. Accordingly, if the curvature of the surface of a bottle to be silk-screen printed is not the same as that of a gear or toothed sector used, any letters printed will be distorted. For example, if the bottle radius is less than that of the toothed sector, the letters will be somewhat shortened. On the other hand, if the radius of the print receiving surface is greater than that of the toothed sector, the letters will be somewhat elongated.
In addition to the silk-screen printing apparatus disclosed in the above patents, which are believed limited to the printing of only one curved surface of an oval-shaped object, or which show the silk-screen printing of two surfaces in side-by-side relationship, we are aware of apparatus developed for the printing of the two sides of an oval-shaped article. The printhead of this apparatus, however, comprises a single squeegee using a very long printing stroke, made possible by a rather large planetary gear system. It is costly to tool, cannot be used on a universal machine, and is not readily convertible from the printing of oval-shaped cylindrical objects to round cylinders or flat printing.
Accordingly, none of the prior art of which the present inventors are aware disclose silk-screen printing apparatus wherein a multiple number of curved surfaces of an article whose periphery is defined by a multiple number of curved surfaces can be printed in sequential manner, at one printing station. Thus, there still remains the need for such a silk-screen printing apparatus and, in particular, silk-screen printing apparatus that is capable of printing both curved, peripheral sides of an oval-shaped article such as the commonly used plastic and glass bottles.